Baucus is the first top Democrat to publicly voice fears about the rollout of the new health care law, designed to bring coverage to some 30 million uninsured people through a mix of government programs and tax credits for private insurance. Polls show that Americans remain confused by the complex law, and even many uninsured people are skeptical they will be helped by benefits that start next year.

A six-term veteran, Baucus expects a tough re-election in 2014. He’s still trying to recover from approval ratings that nosedived amid displeasure with the health care law in his home state.

He said he’s “very concerned” that new health insurance marketplaces for consumers and small businesses will not open on time in every state, and that if they do, they might just flop because residents don’t have the information they need to make choices.

“The administration’s public information campaign on the benefits of the Affordable Care Act deserves a failing grade,” he told Sebelius. “You need to fix this.”

Responding to Baucus, Sebelius pointedly noted that Republicans in Congress last year blocked funding for carrying out the health care law, and she had to resort to raiding other legally available departmental funds.

The administration is asking for $1.5 billion in next year’s budget, and Republicans don’t seem willing to grant that, either.

At one point, as Sebelius tried to answer Baucus’ demand for facts and figures, the senator admonished: “You haven’t given me any data; you just give me concepts, frankly.”

“I don’t know what he’s looking at,” Sebelius told reporters following her out of the room after Baucus adjourned the hearing. “But we are on track to fully implement marketplaces in Jan. 2014, and to be open for open enrollment.”

That open-enrollment launch is only months away, Oct. 1. It’s when millions of middle-class consumers who don’t get coverage through their jobs can start shopping for a private plan in the new marketplaces. They’ll also be able to find out if they qualify for tax credits that will lower their premiums. At the same time, low-income people will be steered to government programs, mainly an expanded version of Medicaid.

But half the states, most of them Republican-led, have refused to cooperate in setting up the infrastructure of Obama’s law. Others, like Montana, are politically divided. The overhaul law provided that the federal government would step in and run the new markets if a state failed to do so. Envisioned as a fallback, federal control now looks like it will be the norm in much of the country, straining resources.

Administration officials say their public outreach campaign will begin in earnest over the summer. They question the wisdom of bombarding consumers with insurance details now, when there’s not yet anything to sign up for. Baucus said in his state, that vacuum has mostly been filled by misinformation.

While some other Democratic lawmakers have privately voiced similar frustrations, most have publicly lauded Sebelius for her department’s work. Democrats from reliably blue states have less to worry about, since their governors and legislatures have embraced the law and are working to make it succeed.

In Montana, the legislature rejected a state-run insurance market proposed by then- Gov. Brian Schweitzer, a Democrat, in 2011. The new Democratic governor, Steve Bullock, is still trying to salvage a compromise on expanding Medicaid.

Republicans are certain to remind Montana voters next year that Baucus’ fingerprints are all over the health care law, even though a similar strategy failed to knock off fellow Democratic Sen. Jon Tester last year.

After the hearing, Baucus’ office clarified that he still thinks the Affordable Care Act is a good law, but he questions how it is being carried out.